The present invention relates to image bearing templates for masking or otherwise modifying the light image to which photographic film is exposed in a camera, and more particularly, it concerns such templates adapted to be used with instant film cassettes.
The current state-of-the-art relative to information or image bearing templates of the general class which includes the present invention are exemplified by the disclosures of U.S. Pat. Nos. 3,916,423 to Ueda et al. and 4,268,144 to Wheeler. In both of these patents, a substantially transparent template or mask having light blocking information or images thereon is adapted to be inserted in an exposure aperture or exposure window of commercially available instant film assemblages in which each of a succession of individual film units supplied in a cassette are advanced to the camera's focal plane as established by a forward wall of the cassette in which the exposure window is formed.
In the Ueda et al. patent, the template or mask is formed by a relatively thick and rigid plate of glass or similar material. In one form, the rigid template of Ueda et al. is a rectangular body dimensioned the same as the exposure window with four outwardly directed projections on the side edges intended to stress the material of the film cassette forming the exposure window to hold the template in place. In another form of the rigid template of Ueda et al., insertability of the rigid plate into the window is enabled by forming the major body of the plate with peripheral dimensions somewhat smaller than the film cassette window so that tabs projecting from opposite sides of the plate can be inserted through the window and will underlie the wall of the cassette housing in which the window is formed. The thickness of the plate causes diffraction of the subject image and results in displacement of the objective focal plane from the surface of the uppermost film unit in the cassette. Sharpness of the subject image can be accommodated by a combination of restricting the thickness of the tabs holding the plate in the window and selecting the index of refraction of the material from which the plate is formed to correct for displacement of the objective focal plane from the surface of the uppermost film unit.
The Wheeler '423 patent employs a relatively thin and pliant template having projecting tabs extending from three sides and adapted to underlie the cassette's forward wall in which the exposure window is formed. To retain the template against movement in one direction with an underlying film unit as the latter is ejected from the cassette for processing after exposure, a leading edge of the template is formed with a central, generally up-struck limit tab. To otherwise orient the template in relation to the exposure window Wheeler relies on edge portions of the thin sheet which, of necessity, fit within the cassette with clearance space between the template edges and the side walls of the film cassette. Also, insertion and removal of the Wheeler template requires manipulation at the image surface of the template. Further, the Wheeler template does not include means for preventing movement of the template toward the cassette's trailing end wall.
Other examples of image bearing templates may be found in U.S. Pat. Nos. 4,655,570, 4,816,848 and 4,894,671.
In light of the prior art, there exists a need for a thin image bearing template which does not distort or rely upon the resiliency of the exposure window frame in a film cassette for retention or insertion of the template, which insures both longitudinal and lateral positioning support of the template in the exposure window and which facilitates insertion and removal of the template without excessive manual contact with the image surface of the template.